Can Lipo Alarm Save Your Battery?

[dogfart]

I have a Lipo Alarm. It is set to go off at 21 V. It worked fine this morning (but I ignored it, and crashed, because I thought it was malfunctioning since I had just installed what I thought was a fully charged battery). Since I have a very good system for making sure that I recharge my batteries after every flight, I am pretty sure I had charged this battery before I installed it. My guess is prior to this I must have ruined the battery by over-discharging it. (I sometimes forget to start the timer that's built into my DX7.) Can I use my Lipo Alarm to warn me that I am about to over-discharge my battery by setting it to go off at a lower voltage? If so, what should I set it to? I am running Flightpower Evo Lites 6S, 5,350 mAh, 22.2 V, 17 Cs.

[TheJackal]

Any Lipo alarm is useless if you ignore it!?!?!?
If it is set at 21V isn't that the safe voltage for your battery, or are you saying you want to lower the alarm to eek out more flying time?

[Coolice]

Hey,

Your running a 6s 5350mah LiPo pack looking at your voltage.

Your lipo alarm needs to be set at 6 x 3 volts = 18 volts alarm set point to save the LiPo's.

Remember any LiPo cell must not be discharged below 3 volts per cell to remain in peak performance and have a reasonable life span. a 6s packs got 6 LiPo cells and so it's 6 x 3 to get the safe voltage.

I'd suggest setting the voltage monitor to 18.5 volts to be safe as it is the very last few MAH that kills a battery both in discharge and charge cycles. At this voltage as well when you land and switch off the drive motor, the current load will be removed and the packs overall voltage will rise slight meaning you will be even further into the safety zone.

One observation with LiPo alarms/lights etc. is when the outside flying temperature is low this can effect the alarms reading of the pack, LiPo's like to be at an optimum temperature to provide the max output.
Plus always make sure you start off with a freshly charged LiPo, eg. no half charged ones so the LiPo alarm does not set itself to a wrong cell count perhaps.

Also another indication to land is a significant decrease in head revs, with experience you can visually & audioably detect a sudden drop in rotor rpm's and this is the time to land asap.
.

[Pinecone]

Efliernz ships his alarms set to alarm at 3.3 - 3.4 volts per cell. I find that is a good number to not go below 80% draw on the pack.

And yes, if you ignore the alarm, it will not save your pack. The whole idea of using both the timer and the alarm to catch things exactly like you did, using a not fully charged pack.

But when the alarm goes off, LAND, and then figure out what is going on.

[dogfart]

Thank you for the advice everyone. That answers my question - the alarm should (in theory) both prevent over-discharge, and allow time to land in case of a low-battery situation. I have a very good system for being sure that I recharge my batteries after every flight. And, I know my charger had replaced something like 4,600 mAh in one battery (I assume the one that I ruined). But, prior to that charge cycle the alarm did NOT go off! It should have, right?

[th3tick]

Your lipo alarm needs to be set at 6 x 3 volts = 18 volts alarm set point to save the LiPo's.

With that setting, it's not a "save your battery" alarm, but one which let's you know you've damaged it.

I tend to go with, as Pinecone/EFlierNZ do with 3.3-3.4, plus another half volt or so total. That way it beeps when it's getting close during harder maneuvers, and goes full-on when it's time to land. So for 3S, 10.5, and 6S, 20.5.

John

[dogfart]

With that setting, it's not a "save your battery" alarm, but one which let's you know you've damaged it.

I tend to go with, as Pinecone/EFlierNZ do with 3.3-3.4, plus another half volt or so total. That way it beeps when it's getting close during harder maneuvers, and goes full-on when it's time to land. So for 3S, 10.5, and 6S, 20.5.

John

Thanks John. So if I understand, with 6S, setting the alarm at 21V (.5 V higher than the 20.5V you suggest) should work as a "save the battery" alarm, right?

[th3tick]

Thanks John. So if I understand, with 6S, setting the alarm at 21V (.5 V higher than the 20.5V you suggest) should work as a "save the battery" alarm, right?

Yeah, that's just being even further careful. You need to balance the flight time vs. endangering packs. All you're really after is never causing it under load to have a cell go below 3.0V. With 20V for 6S, you're already adding 2V of safety margin, since it dips under load, and you may not see or hear the alarm for those. By the time it's full-on with my setup, I know it's been a little lower on occasion in the danger zone of 18-20V.

Then, I judge how well it was by the voltage it's at after it's cooled and rested. It should be about 22.2V at rest, and if it's lower, you probably over-did it a bit.

You can then use all that to come up with a timer setting so you'll know when it's about to go off. I tend to use the alarm as my "oops" alert, rather than my primary notification that it's time to land. There are times where you're just too focused on flying to notice the light/sound, not to mention the sunlight or angle can mask the light, and the heli's own noise can cover an alarm's sound. Still, I wouldn't put a heli in the air without one. It's cheap insurance.

John

[wren1702]

Based off of your 600 XL thread, I'd say that your motor shaft broke in flight, causing your crash....not a low battery!

[dogfart]

Based off of your 600 XL thread, I'd say that your motor shaft broke in flight, causing your crash....not a low battery!

Thanks for that thought. But I think the battery went out based on the fact the lipo alarm had been flashing for a while.

[wren1702]

Very odd that a crash would cause the motor shaft to break. If the motor shaft broke, it could have caused the rotor inside the motor to drag against the case.....causing amps to go way up and pulling your battery down to a low voltage. Then the shaft broke all the way and it stopped running. Just a thought. I've just never heard of a shaft breaking during a crash.

[Pinecone]

Thanks John. So if I understand, with 6S, setting the alarm at 21V (.5 V higher than the 20.5V you suggest) should work as a "save the battery" alarm, right?

Actually 3.3 volts per cell is 19.8 volts, round to 20 volts to easily set the thing, then add 0.5 volts safety margin and you get the 20.5.

Some packs will run about 21 volts under load, so setting at that point may give you a false signal.